"Manyū Hiken-chō" is set in an alternate historical Japan where the size of a woman's breasts determines her social status, power, and influence. The story revolves around the Manyū Clan, a secretive organization that wields control over society by monopolizing techniques to manipulate breast size. The clan's ultimate weapon is the Manyū Hiken, a scroll containing forbidden techniques that can alter a woman's body.

The protagonist, Chifusa Manyū, is the heir to the clan and a skilled swordswoman. Despite her position, she harbors doubts about the clan's oppressive practices and its exploitation of women. When she discovers the Manyū Hiken, she decides to steal it and flee, aiming to dismantle the clan's dominance and challenge the societal norms that prioritize physical appearance over individuality. Her actions set off a chain of events, as the clan dispatches assassins and warriors to retrieve the scroll and eliminate her.

Throughout the series, Chifusa encounters various women who have been affected by the clan's influence, including Kaede, a former clan member who becomes her ally, and Ouka, a rival warrior determined to reclaim the scroll. The narrative explores themes of power, identity, and rebellion, as Chifusa fights to protect the scroll and liberate women from the oppressive standards imposed by the Manyū Clan. The story blends action, humor, and social commentary, presenting a satirical take on societal beauty standards and the consequences of conformity.